This study will test the hypothesis that fetal temporary tracheal occlusion, when compared to standard postnatal care for the treatment of severe congenital diaphragmatic hernia, will improve survival and quality of life. Although a controlled randomized trial of any fetal treatment poses great difficulties, it is time to establish whether this innovative therapeutic modality should be pursued or abandoned. It is the general aim of this proposal to perform a clinical trial to assess the efficacy and safety of fetoscopic tracheal occlusion for the treatment of severe CDH. This is a prospective randomized controlled trial comparing two groups; those who undergo endoscopic fetal tracheal occlusion between 24 and 28 weeks' gestation, and those who deliver at or near term and receive standard tertiary postnatal care. The sample population is a subset of fetuses with CDH who, by applying selected criteria developed in previous experimental and clinical studies, are deemed to have an 80% mortality rate: isolated CDH diagnosed before 25 weeks' gestation with liver herniated into the hemithorax and low lung-to-ratio (LHR) as outcome predictors